Process for cleaning and plating ferrous metals



United States Patent O PROCESS FOR, CLEANING AND PLATING FERROUS METALSWalter R. Meyer, Hamden, Conn., assignor to Enthone, Incorporated, NewHaven, Conn., a corporation of Connecticut "No Drawing. ApplicationDecember 9, 1955 Serial No. 551,977

'19 Claims. (Cl. 204-145) deteriorate nonferrous coatings on iron andsteel when rust removal from such surfaces is done. Another shortcominginherent in automatic plating operations involving acid pickling is, thestrong tendency of the work to rust after pickling and beforemetaldeposition. Prior attempts at nonacid pickling have been slow, tediousand only partly successful. This application is a. continuation-in-partof application Serial No. 323,696, filed December 2, 1952, nowabandoned.

A primary object of ,this invention is to provide a process which willselectively remove rust from the surfaces of' ferrous metals withoutaction whatsoever on the base metal.

Another object is to provide a process for accomplishingcleaning andrust-removal from ferrous metals in a single operation.

Another object is to provide a process for the alkaline cleaning andderusting of ferrous metals which eliminates the objections inherent inacid-pickling operations.

I havediscovered a process where, in the presence of certain complexingand chelating agents, foreign matter, including rust, dirt, scale,grease, and the like, are. rapidly removed from the surfaces of themetal While passing a current through an alkaline solution of thecomplexing agent at a pH' of 10.0 or greater while the articles treatedare madethe cathode.

The invention is valuable for a variety of metal-treating operations.",For example, it is suitable for removing the oxides from ferrous metalarticles including,,with or without the aid of a supplemental treatment,heavy electrically conducting deposits and scales of black oxide ofiron. It removes rust frorn iron and steel plated or otherwise coatedwith another metal, sujchas steel electroplated with nickel, chromium,silver, zinc, cadmium and tin without significantly dissolving the plateor coating. It can be used to clean molds, such as molds for rubberarticles, plastic articles, etc., stripping ofi' remnants of the rubber,plastic, etc., left on them. It also strips paint, resins, and varnish,and removes oil, grease, carbon, smut, and superficial dirt. It

is suitable for cleaning off oil and grease, etc., and for deoxidizingferrous articles in preparation for further treatment, such as painting,phosphating, electroplating, ete., in a single operation inmostinstances as contrasted with the two operations now commonly employed,one for cleaning and another for removing rust and scale, and also to doso without attacking the underlying metal 2,915,444 Patented Dec. 1,1959 as the acid pickles tend to do. However, it is not well applicableto stainless steel for this latter purpose.

Solutions of this invention are vehicles from which various metals, suchas zinc, cadmium, silver, copper, iron and tin can be electroplated outand these solutions also accomplish cleaning and deoxidizing. Forexample, solutions of this invention can be used for cleaning, oxideremoval and plating whereby the article to be treated is immersed in onesolution in contrast with three or more solutions normally required. Aferrous article coated with grease and rust when immersed in solutionsof this invention can be seen to first have the grease removed.Following this the oxide is removed and as soon as oxide has beenremoved, the metal will plate out. Considerable practical use hasresulted from this invention for plating of articles difficult to rinse,such as large cylinders with small openmgs.

In accordance .With the invention, 1 have discovered that ferrous metalscan be cleaned of oils, grease, and the like, deoxidized, and strippedof nonmetallic coatings by subjectingthe articles to electrolysis in astrongly alkaline aqueous solution of a water-soluble complexing orchelating agent for iron oxides, while the articles are made the cathodefor at least part of the time during electrolysis. An alkylolamine, suchas triethanolamine, will function eifectively as the complexing agent orcan be preferably employed to augment the action of other complexingagents, through its ability to solubilize the iron in the high pH range.The addition of an alkaline cyanide salt to the solution tends to speedthe effective action of the solution containing the complexing agent.The operation may be at room temperature, although elevated temperaturesappear to accelerate the rate of reaction. Various metals, for examplesuch as those mentioned above, are soluble in the solution, and whenpresent may be electroplated out onto the articles; the invention can beused solely for cleaning and desxidizing or jointly for cleaning,pickling, and/or stripping and electroplating so that a ferrous articlecan, at the same time, be prepared for electroplating, and thenelectroplated in a single continous operation. When black 0X- ides ofiron, such as heat treat scale, composed of Fe O are to be removed, ithas been found advantageous to make the article alternately the anodeand then the cathode, whereas, when the oxide is nonconductive ferrictypes of oxide, best oxide removal is accomplished by making the workthe cathode solely.

The operation, seems to dissolve the ferrous and ferric oxides, and itsaction in removing these oxides as well as light greases, oils andsuperficial dirt is remarkably rapid, a matter of seconds or a fewminutes, depending upon the current density employed. With mostarticles, therefore, a single treatment with the present invention issufiicient for complete cleaning.

The complexing or chelating agents used in the practice of the inventionmay be selected from a large class of water-soluble organo hydroxy,organo amino and amino hydroxy compounds found to be effective withinthe specified conditions of alkalinity, and while the iron and steelarticles are made the cathode during treatment. Preferably, thecomplexing agents are organic compounds provided with at least twohydroxyl or amino groups or one hydroxyl and one amino group adjacentlylocated in the molecule to produce a complex or chelate ring with ioniciron in the form of ferrous or ferric 0xides, while not affecting theunderlying molecular iron. Whether this action actually occurs duringthe course of the reaction and under the conditions specified, orwhether the agents merely combine with the ferrous and ferric ions insome other manner, is immaterial to a definition of the invention whichoperates successfully for the cleaning and derusting of the ferrousarticles under the specified conditions.

Among the complexing agents suitable for the practice of the presentinvention, the following groups of derivatives have been found tooperate successfully under the conditions of high alkalinity and whilethe ferrous articles are maintained the cathode for at least a portionof the treatment:

(1) Open chain polyhydroxy compounds with hydroxy groups in l, 2 or 1, 3positions, preferably the 1, 2 positions, such as ethylene glycol,propylene glycol as well as polyol compounds, including glycerine,mannitol, sorbitol, fructose, sucrose, glucose, and starches.

(2) Hydroxycarboxylic acids containing at least two hydroxy groups oneof which is spaced no further than the beta position from the carboxylgroup. These compounds include such materials as glyceric, saccharic,tartaric, and gluconic.

(3) Amino carboxylic acids where the amino grouping is in the alpha orbeta position such as glycine, alanine and betaalanine.

(4) Diamines where the amino groupings are on adjacent carbons or oncarbons in the 1 and 3 positions. These include ethylene diamine,propylene diamine, diethylene triamine and other condensation productsof ethylene diamine.

(5) Acetic acid substituted ammonia compounds, such as ammonia diacetateand ammonia triacetate.

(6) Ethylene diamine diacetic acid salts, ethylene diamine triaceticacid salts and ethylene diamine tetraacetic acid salts. They alsoinclude compounds where one or more of the acetate groupings is replacedwith an ethanol grouping, such as hydroxyethyl ethylene diaminetriacetic acid salts, and dihydroxyethyl ethylene diamine diacetic acidsalts.

(7) Hydroxyamino compounds or alkylolamines, such as ethanolamine,diethanolamine, triethanolamine and corresponding propanolamines, aswell as related compounds such as aminoethylethanolamine.

For cleaning and deoxidizing, the solution consists essentially of thereaction products of the following agents in aqueous solution per literof solution:

An alkali hydroxide or hydroxides, for example sodium hydroxide orpotassium hydroxide or a mixture of these two, sufficient in quantity togive the ultimate solution a pH above ten (10), and preferably higher.By weight there may he, say, from five (5) grams to four hundred (400)grams. The maximum permissible quantity however is that which leaves thesolution with only sufiicient solubility to dissolve sufiicient of theother active agents. Preferably I use between twenty-five (25) and twohundred (200), and ordinarily about one hundred twenty (120) grams, thisbeing about an optimum value considering the optimum concentrations ofthe other active agents.

Iron ion complexing agent, from about five (5) grams to saturation. Itspreferred range appears to be from about thirty (30) grams to 120 grams.

One or more alkali cyanides (such as, for example, sodium cyanide orpotassium cyanide), from none at all to saturation. About one hundredtwenty grams (120) is a suitable concentration.

Water sufiicient to make one liter of solution.

The bath or solution can be formed by dissolving in water such of theforegoing agents or equivalents of them as may be desired in anyinstance. The iron ion complexing agents are readily soluble either inwater at room temperature or in the alkaline solution having a pH of atleast 10.0. In the case of carboxylic acid complexing agents, thealkalized salts are readily soluble in water, whereas, the acidsthemselves are directly soluble in the alkalized solution. It is usuallymore convenient where possible to use the iron ion complexing agent inthe form of its salt. Also, the TEA is an oily liquid which ishygroscopic, while its hydrochloride is a dry powder. For this reason, Imay prefer to use the hydrochloride formrather than the liquid.

However, the two, three or four of such active ingredients (i.e.,however many may be used in any instance) may be mixed in the form ofdry powder (the TEA being in the form of the hydrochloride), and storedin this form. The relative proportions of the active agents oringredients comprising the dry composition may be various of course,just as in the case of a solution and as appears above. A suitablemixture of this form is, the proportions being by weight; sodiumhydroxide, thirtysix (36) parts; iron ion complexing agent, thirty (30)parts; and sodium cyanide, thirty-four (34) parts. A cleaning andpickling solution containing about such optimum concentrations of theactive constituents can be made by dissolving from about fifty (50)grams to about four hundred (400) grams of such a mixture, preferablyabout three hundred sixty (360) grams, in suflicient water to make one(1) liter of solution.

As before indicated, the cleaning operation in the ordinary case, e.g.,when the oxides present are mostly the ferric oxides, such as heavyrust, may consist only of subjecting the piece or article toelectrolysis for some seconds or a few minutes in a solution of thenature indicated above, the piece or article being the cathode of thecell for at least a part of the time. However, when the oxide is heavyand its pores filled with oil, the action of the electrolysis tends tobe somewhat slower, and then can be speeded up by precleaning to removethe oil or grease. Any ordinary cleaning operation that is sufiicientfor such work is satisfactory for the present purposes; it may be, forexample, simple soaking in solvents, or vapor degreasing, orelectrolytic alkali cleaning, and I prefer anodic alkali cleaning. Alsowhere considerable black oxide (Fe 0 is present, including welding andheat treatment scale, or where nonporous coatings of paint or othernonmetallic coatings are continuous over substantial parts of the areato be cleaned, the piece or article can well be treated, or even mayneed to be treated to break up the continuity of the foreign matter andgive the present solution access through them. For example, some partsscaled by heat treatment can be descaled successfully by the presentoperations if first they are soaked in a strong acid, e.g., hydrochloricacid or sulphuric acid, for a few minutes; for example, in 25% to 50%commercial hydrochloric acid for from one to five minutes. The acid soakrenders the scale porous and thus permits the solution to penetrate it.Again, continuous areas of paint, etc., may be broken up mechanically,e.g., by tumbling in a barrel, with or without the aid of steel balls,by flexing, and the like.

For the electrolysis, the anode or anodes are made of carbon bypreference, since anodic action in the present solution dissolves mostmetals, and additionally the dissolved metals may plate out onto thearticle being treated.

The bath temperature may be substantially any readily availabletemperature, that is to say from about 60 F. to the boiling temperatureof the solution. Speaking generally, the higher the temperature, themore rapid is the deoxidizing and cleaning operation, but also thegreater the tendency for the bath or solution to break down, and this isespecially true when cyanide is present in the solution. Preferably, Ido not exceed 130 F.; a temperature of 120 F. is quite satisfactory, inmost instances at least; even at this latter temperature there is somedecomposition of the bath due to temperature, and longer life isobtained by running the solution from 70 to F. Insofar as may benecessary or desirable, the bath can be heated by immersion electricheaters or otherwise of course, as will be understood fromelectroplating practices. However, the current flow tends to heat thebath, and at high current densities it may be necessary to cool the bathby cooling coils or otherwise to prevent the temperature rising above adesired value.

The current density, i.e., the current density at the area or areas ofthe work being treated can vary'between wide'limits, e.g., from sayone-tenth (0.1) ampere per (100) amperes per square foot, andcustomarily about fifty (50) amperes per square foot is satisfactory.

For the removal of rust (ferric oxide) for example, the current may bedirect current, the' piece or article being treated being the cathodeofthe electrolytic cell for the entire periodof the electrolysis. Byreversing the direction of the current flow occasionally however, sothat the work, i.e., the piece or article being treated, is made theanode occasionally or periodically, the attack may be made somewhat:heavier and the operation brought .to completion somewhat more quickly,especially when the oxides, scales and other foreign matters arethosewhich are not so readily and directly affected by cathodic treatment.Alternating current of the common commercial frequency .(60 cycles persecond) ,may be used, but frequericies lower than this are preferable,and in fact down to very low frequencies of ten cycles per minute orless. Also, nonsymmetrical reversals may be found preferable tosymmetrical in some instances, depending on the nature of the foreignmatter to be removed and the base metals. During the anodic periods, theoperation removes surface smut and also seems to cause pores in andundermine the foreign matters, thereby giving the solution access to andunderneath the foreign matters during the cathode periods. The relativelengths of the cathode periods and the anodic periods may be selectedwith this in mind; i.e., the less effective the cathode action in anyinstance, the longer to be the time periods chosen for the anodicaction. Such periodic reversals that the work is the; cathode forperiods of about thirty seconds each and the anode for periods of aboutten (10) seconds each, is quite effective usually.

So far as concerns maintenance of the solution, such of the iron as istaken into the solution is readily disposed of. The dissolved iron maybe plated out either automatically as it were, during the course of andas an incident accompanying the deoxidizing, or as it were by extendingperiods of deoxidizing a little. When the cyanide ispresent,'accumulating iron is precipitated as an iron cyanide complex.Excepting for such loss of cyanide, the'principal loss of solution andits active agents seems to be that which occurs through drag-out,leakage, spray and the like. In maintaining the solution therefore, thesolution may be analyzed occasionally for cyanide, and the cyanidereplaced as may be necessary to keep the cyanide concentration within aneffective range; the range being a rather wide one, as appears above,this can be done readily and without an undue amount ofattention. As tothe remainder of the active agents, it is necessary only to analyze thesolution for, say, the hydroxide occasionally and replace as necessaryto maintain the hydroxide concentration within the range selected forit,.and at the same time, i.e., whenever replacing hydroxide, add morecomplexing agent, and in say, the same relative proportions. as wereused in making up the original mixture. Water may be added as necessaryto maintain an adequate volume of the solution.

Example I A simple example of deoxidizing will serve to illustrate theforegoing. Assume that a cast iron piece has a heavy thick coating ofblack oxide, perhaps with a material amount of adsorbed oil: If desired,the piece may be cleaned in any simple way to remove superficial dirt,

6 loose rust, etc. such as :vapor degreasing the piece until freevofoil. Then immerse in an alkalineaqueous solution previously made from adry mixture containing sodium hydroxide, thirty-six (36) parts,tetrasodium salt of ethylene diamine tetraacetic acid, fourteen (14)parts;

TEA hydrochloride sixteen (16) ,parts; and sodium cyanide, thirty-four(34) parts, using about three hundred sixty (360) grams of the mixturefor each liter of the solution.

at such a voltage that the current .density at the piece being treatedis about fifty (50) amperes per square foot..

Reverse the direction .of the flow of thecurrent. repeatedly so that thepiece being treated is the cathode of the cell for periods ofabout'thirty (30) secondseach and is the anode for intervening periodsof about ten (10) seconds each. By heating or cooling, maintain thetemperature of the bath about 120 F.; unless the volume of the bath islarge relative to the size of the piece being treated, probably thiswill require the bath to be cooled. Continue this treatment until thesurface of the piece is completely freed of the oxide, or freed of theoxide to such an extent as maybe desired; complete freeing of the oxidemay take from two (2), minutes to as much as fifteen (15) minutes if thescale is dense and deep; or possibly up to thirty (30) minutes. When theaction is completed, remove the piece from the solution and rinsethoroughly in running water. If desired, the surface of the piece can beneutralized by then dipping in an acid solution, say an aqueous solutionof about seven and one-half (7.5) grams of chromic acid (CrO per literof.

water, and then rinsing again in water.

Example 11 Example III A similar solution as that employed in Example IIwith the addition of one hundred grams per liter of sodium cyanide wasused in cleaning rusty steel. The additionof the sodium cyanideshortened the derusting time to approximately one and one-half (1.5)minutes.

Example IV A solution was prepared containing sodium hydroxide,approximately one hundred (100) grams per liter, sodium cyanide,approximately seventy (70) grams per liter and as complexing agents,ethylene glycol, approximately eighteen 18) grams per liter, andglucose, approximately ten (10) grams per liter. 130 F. Corroded rustysteel was immersed in the solution, and used as the cathode, while acarbon electrode similarly immersed served as the anode. A currentdensity of approximately twenty-five (25) amperes per square footaccomplished the complete removal of rust, leaving a clean surface in aperiod of about .two and one-half (2.5) minutes.

Example V A solution was prepared containing sodium hydroxide,approximately two hundred forty (240) grams per liter, and mannitol asthe complexing agent, approximately one hundred twenty gramsper liter.Temperature was F. Rusty steel made the cathode in.this bath with acurrent density the same as in Example IV re sulted in complete cleaningin a period of about seven (7) minutes.

Temperature was 7v Example VI A solution containing the same mixture ofingredients as employed in Example V, with the addition of sodiumcyanide, about one hundred twenty (120) grams per liter accomplishedcomplete cleaning of the metal surfaces in a period of about four (4)'minutes.

Example VII A solution bath was prepared containing sodium hydroxide,about two hundred forty (240) grams per liter and hydroxyethyl ethylenediamine triactic acid, one hundred twenty (120) grams per liter.Temperature was 130 F. Heavily rusted iron was made the cathode in thissolution during passage of a current density of twenty-five (25) amperesper square foot. The metal was thoroughly cleaned in a period of aboutfive (5) minutes.

Example VIII Example VII was repeated with the addition of sodiumcyanide, about one hundred twenty (120) grams per liter to theelectrolyte which reduced the period of treatment to approximately four(4) minutes.

Example IX tions as specified in Example VIII was approximately five (5)minutes.

Example X The addition of sodium cyanide one hundred twenty (120) gramsper liter reduced the treatment period in Example IX to approximatelyfour (4) minutes.

As pointed out before, the solution of the invention can be used also asa vehicle from which certain metals can be plated out onto certainmetals. Those which can 'be so plated out are such as cadmium, zinc,tin, copper and silver. On the other hand, by adding such a metal to thesolution, cleaning, deoxidizing and plating can be done in onecontinuous operation when the foreign matter is electricallynonconducting, the electrolysis being continued, of course, beyond thecleaning and/or deoxidizin'g stage for so long as may be necessary inorder to secure the desired thickness of deposit, and the current beingmaintained wholly unidirectional ordinarily with the work the cathode,at least from the time the cleaning and deoxidizing has been completed.When the foreign matter is electrically conducting, for example aconducting scale, and is not removed by unidirectional current with thearticle the cathode, a plate can be laid down on the foreign matter. Theconcentration of the metal to be plated out may be between say one (1)gram and fifty (50) grams per liter of the solution. The higherconcentrations are rather wasteful, however, because of losses due todrag-out. Ordinarily, I use between about eight (8) grams per liter andthirty-two (32) grams per liter of the respective metal, and bypreference about fifteen grams per liter. Zinc can be added to thesolution as zinc sulphate (first dissolved in water and this solutionadded to the primary solution), or as zinc oxide or zinc cyanide. Zinccan be deposited on low carbon steel, but does not plate well onto castiron or high carbon steel. Cadmium plates out onto low carbon and highcarbon steel, and cast and malleable iron. Cadmium can be added to thedeoxidizing solution as cadmium sulphate, cadmium oxide or cadmiumcyanide. Tin can be added as sodium stannate or sodium stannite. Coppercan be added in the form of sulphate, cyanide or carbonate. It will beunderstood of course that the foregoing salts are mentioned as examples.To secure complete dissolution of the metal salt, or perhaps avoidrobbing the bath of cyanide (or rather of the radical CN), an additionof say, sodium'or potassium .cyanide can be tions as the cleaning anddeoxidizing is done, e.g., at the same current density and solutiontemperatures, except that in the case of copper or tin the solutiontemperature should be about 150 F., and in the case of other of themetals also, solution temperatures higher than those of cleaning anddeoxidizing may be desirable, or perhaps necessary in some instances,especially for higher plating efiiciency. However, temperatures above,say about 130 F. tend to faster decomposition of the solution, aspointed out above.

As a specific example, assume that a piece of low car- I bon steelcarrying red rust and no electrically-conductive scale, is to be platedwith zinc; Form a solution of the dry mixture of the four activecleaning and deoxidizingagents specifically described above, in Water,using about three hundred sixty (360) grams of the mixture for eachliter of the final solution. To this solution, add about nineteen (19)grams of Zinc oxide (ZnO) for each liter of the final solution. Add alsoto the solution so much sodium cyanide (NaCN) as may be necessary toproduce complete dissolution of the zinc oxide. Then imrnerse the piecein the solution, together with a carbon electrode. Apply direct currentto the two, making the piece the cathode, and with the voltage such thatthe current density at the piece is about fifty (50) amperes per squarefoot, and maintain the temperature of the solution at about F. Theaction removes the rust and scale from the piece and also any light oiland grease there may be on it, and simultaneously deposits the zinc as aplate. Continue the current flow under the same conditions until theelectroplate of zinc has reached the desired thickness. Then remove thepiece from the solution, and rinse it well with running water.

As metal is abstracted from the solution in plating (zinc in theforegoing example), further salt of the metal (e.g., zinc oxide) can beadded to the solution from time to time to compensate for the loss andmaintain the metal concentration within the desired range as successivearticles are plated, or an anode of the metal being plated out can beused.

As successive articles are treated, oil may collect on the top of thesolution, and foreign matter, etc. from the pieces being treated maycollect or sludge in the bottom of the tank. The oil can be skimmed orotherwise taken away from time to time and also the sludge more or lesscleaned out of the tank from time to time.

Occasional anodic treatment of low carbon ferrous metals in the solutionof the invention not only cleans the surface of smut but produces aclean surface which facilitates the formation of a good bond insubsequent electroplating.

Also while above I have described the composition of this invention as adry mixture of the active agents, it

-33... line/a ing oxide of iron, from ferrous metals which consists insubjecting the metal to electrolysis in a solution formed by dissolvingin water alkali hydroxide, about one hundred twenty (120) grams perliter of solution, tetra alkali salt of ethylenediaminetetraacetic acid,about forty (40) grams per liter of solution, triethanolamine, aboutfifty (50) grams per liter of solution, an alkali cyanide, about onehundred twenty (120) grams per liter of solution, and the metalundergoing treatment is made the cathode.

2. The process of removing foreign matter, including oxides of iron fromferrous metals which comprises subjecting the metals to electrolysis asthe cathode in an alkaline aqueous solution having a pH of above 10.0,and containing an alkali gluconate in an amount of from about five gramsper liter to saturation.

3. The process of removing foreign matter including oxides of iron fromferrous metals which comprises subjecting the metals to electrolysis asthe cathode in an alkaline aqueous solution having a pH of above 10.0and containing an agent selected from the class consisting of alkaligluconate, alkali saccharate, ethylene diamine diacetic acid salts,ethylene diamine triacetic acid salts, ethylene diamine tetraacetic acidsalts, hydroxy ethyl ethylene diamine triacetic acid salts, andtriethanolamine, said agents having the common property of complexingiron into soluble form, and being present in an amount of from aboutfive grams per liter to saturation.

4. The process of removing foreign matter including oxides of iron fromferrous metals which comprises subjecting the metals to electrolysis asthe cathode in an alkaline aqueous solution having a pH of above 13.0

and containing an agent selected from the class consisting of alkaligluconate, alkali saccharate, ethylene diamine diacetic acid salts,ethylene diamine triacetic acid salts, ethylene diamine tetraacetic acidsalts, hydroxy ethyl ethylene diamine triacetic acid salts, andtriethanolamine, said agents having the common property of complexingiron into soluble form, and being present in an amount of from aboutfive grams per liter to saturation.

5. The process of removing foreign matter, including oxides of iron fromferrous metals which comprises subjecting the metals to electrolysis asthe cathode in an alkaline aqueous solution having a pH of above 10.0,and containing an alkali saccharate in an amount of from about fivegrams per liter to saturation.

6. The process of removing foreign matter, including oxides of iron fromferrous metals which comprises subjecting the metals to electrolysis asthe cathode in an alkaline aqueous solution having a pH of above 10.0,and containing an ethylene diamine diacetic acid salt in an amount offrom about five grams per liter to saturation.

7. The process of removing foreign matter, including oxides of iron fromferrous metals which comprises subjecting the metals to electrolysis asthe cathode in an alkaline aqueous solution having a pH of above 10.0,and containing an ethylene diamine triacetic acid salt in an amount offrom about five grams per liter to saturation.

8. The process of removing foreign matter, including oxides of iron fromferrous metals which comprises subjecting the metals to electrolysis asthe cathode in an alkaline aqueous solution having a pH of above 10.0,and containing an ethylene diamine tetraacetic acid salt in an amount offrom about five grams per liter to saturation.

9. The process of removing foreign matter, including oxides of iron fromferrous metals which comprises subjecting the metals to electrolysis asthe cathode in an alkaline aqueous solution having a pH of above 10.0,and containing an akali gluconate in an amount of from about five gramsper liter to saturation and an alkali cyanide.

10. The process of removing foreign matter, including oxides of ironfrom ferrous metals which comprises subjecting the metals toelectrolysis as the cathode in an alkaline aqueous solution having a pHof above 10.0, and containing an alkali saccharate in an amount of fromabout five grams per liter to saturation and an alkali cyanide.

11. The process of removing foreign matter, including oxides of ironfrom ferrous metals which comprises subjecting the metals toelectrolysis as the cathode in an alkaline aqueous solution having a pHof above 10.0, and containing an ethylene diamine diacetic acid salt inan amount of from about five grams per liter to saturation and an alkalicyanide.

12. The process of removing foreign matter, including oxides of ironfrom ferrous metals which comprises subjecting the metals toelectrolysis as the cathode in an alkaline aqueous solution having a pHof above 10.0, and containing an ethylene diamine triacetic acid salt inan amount of from about five grams per liter to saturation and an alkalicyanide.

13. The process of removing foreign matter, including oxides of ironfrom ferrous metals which comprises subjecting the metals toelectrolysis as the cathode in an alkaline aqueous solution having a pHof above 10.0, and containing an ethylene diamine tetraacetic acid saltin an amount of from about five grams per liter to saturation and analkali cyanide.

14. The process of claim 2 wherein the pH of the solution is above 13.0.

15. The process of claim 5 wherein the pH is above 13.0.

16. The process of claim 6 wherein the pH of the solution is above 13.0.

17. The process of claim 7 wherein the pH of the solution is above 13.0.

18. The process of claim 8 wherein the pH of the solution is above 13.0.

19. In a method of electrolytically cleaning a ferrous metal object, thesteps which comprise immersing said object in an aqueous solutionconsisting essentially of an alkali metal hydroxide and at least about0.5 percent of triethanolamine, said solution having a pH above 10, andpassing an alternating current of 60 cycles per second from said objectthrough said solution.

References Cited in the file of this patent UNITED STATES PATENTS1,475,198 Pottholf NOV. 27, 1923 2,565,189 Wernlund Aug. 21, 19512,685,564 Emmett et al Aug. 3, 1954 FOREIGN PATENTS 731,102 Germany Feb.3, 1943 OTHER REFERENCES Transactions of the Electrochemical Society,vol. 65 (1934), pp. 357-360, by R. R. Rogers.

Sequestrenes, Alrose Chem. 00., Providence, R.I., July 25, 1952, p. 27.

3. THE PROCESS OF REMOVING FOREIGN MATTER INCLUDING OXIDES OF IRON FROMFERROUS METALS WHICH COMPRISES SUBJECTING THE METALS TO ELECTROLYSIS ASTHE CATHODE IN AN ALKALINE AQUEOUS SOLUTION HAVING A PH OF ABOVE 10.0AND CONTAINING AN AGENT SELECTED FROM THE CLASS CONSISTING OF ALKALIGLUCONATE, ALKALI SACCHARATE, ETHYLENE DIAMINE DIACETIC ACID SALTS,ETHYLENE DIAMINE TRIACETIC ACID SALTS, ETHYLENE DIAMINE TRIACETIC ACIDSALTS, HYDROXY ETHYL ETHYLENE DIAMINE TRIACETIC ACID SALTS, ANDTRIETHANOLAMINE, SAID AGENTS HAVING THE COMMON PROPERTY OF COMPLEXINGIRON INTO SOLUBLE FROM, AND BEING PRESENT IN AN AMOUNT OF FROM ABOUTFIVE GRAMS PER LITER TO SATURATION.